It’s not always clear where we’ve acquired fitness knowledge—was that fact pounded into you from elementary gym class? Or perhaps you read it in a magazine somewhere. But regardless of its origin, you now follow that advice in your day-to-day, right?

Most people, whether they know it or not, are guilty of following at least one outdated—or just plain lousy—piece of oft-repeated fitness instruction. We talked to fitness experts across the country and scoured medical journals to get to the bottom of some of the most widespread—and flagrant—exercise myths, and give you science-savvy, expert-approved solutions.